1. Field of the Invention
The present invention relates to a method of forming a line-and-space pattern with a microscopic pitch, and more particularly to a method of fabricating a semiconductor device, suitable for the forming of a shallow trench isolation (STI) structure, gate electrodes or wiring patterns.
2. Description of the Related Art
Forming a wiring pattern of line-and-space includes a first pattern forming method by processing a wiring material film and a second pattern forming method by burying a wiring material in grooves of a wiring pattern formed on an insulating film. In the first pattern forming method, a mask is normally formed which has the same pattern as a wiring pattern of line-and-space that is resolvable by an exposure technique. A base film which is a conductive film is formed into a desired wiring pattern using the mask. In the second pattern forming method, a mask is normally formed which has the same pattern as a wiring pattern of line and space that is resolvable by an exposure technique. A base film which is an insulating film is patterned using the mask, whereby grooves are formed. A wiring material is buried in the formed grooves and thereafter, unnecessary wiring material is removed by a chemical and mechanical polishing (CMP) process, whereby a desired wiring pattern is obtained.
A pitch of obtained line-and-space patterns depends upon the resolution limit of the exposure technique in each of the above-described pattern forming methods. With recent acceleration of refinement, however, it has become more and more difficult to refine the pitch by the exposure technique. On the other hand, various methods have recently been suggested for forming a line-and-space pattern having a pitch exceeding the resolution limit of the exposure technique. For example, Japanese patent application publication, JP-A-2006-32648 and U.S. Pat. No. 7,312,158 propose a pattern forming method called “sidewall mask transfer method.” In this method, mask films formed on sidewalls of a first pattern are left thereby to be used as a second pattern. This method can form a line-and-space pattern whose pitch is one-half of a pitch in the exposure technique. However, the aforesaid reduction of the pitch by the exposure technique is insufficient for miniaturization, and a further pitch reduction is necessitated.